The present invention relates to a picture signal converting apparatus and a method thereof suitable for use with a television receiver, a VTR, and so forth.
Conventionally, as television scanning field frequencies, 50 Hz (for PAL system and SECAM system) or 60 Hz (for NTSC system) have been widely used. A field frequency converting technology for converting the field frequency from 50 Hz to 60 Hz or vice versa is known. When the field frequency is converted from 50 Hz to 60 Hz, five fields as input fields should be converted into six fields as output fields. To obtain an output picture that has a smooth motion, a moving vector of an input picture is detected. Corresponding to the detected moving vector, output fields having sufficient time information are formed.
Thus, in the conventional field frequency converting technology, it is necessary to detect a moving vector. In other words, the hardware scale of the apparatus adversely becomes large. Since the accuracy for detecting the moving vector is not so high, the picture may deteriorate due to a moving vector that is incorrectly detected. In particular, an unnatural motion may take place in an output picture (this motion is referred to as jerkiness). In addition, an edge portion of a moving picture may become dull. Although the number of fields may be converted by a linear interpolating process rather than detecting a moving vector, a moving portion becomes dull.
Therefore, an object of the present invention is to provide a picture signal converting apparatus and a method thereof that allow a problem in a conventional field frequency converting technology to be solved.
To solve the above-described problem, the invention of claim 1 is a picture signal converting apparatus for converting a field frequency of an input picture signal in the relation of M and N (where Mxe2x89xa0N; M and N are any natural numbers), comprising:
a class deciding portion for deciding a class for a considered pixel according to a plurality of pixels of the input picture signal, the plurality of pixels being decided according to the considered pixel in a considered field of an output picture signal, the plurality of pixels containing at least a pixel of a field of the input picture signal, the field being placed most chronologically adjacent to the considered field of the output picture signal,
a memory portion for storing predictive information pre-obtained for each class,
a predictive pixel selecting portion for selecting a plurality of pixels of the input picture signal, the plurality of pixels being decided according to the considered pixel in a considered field of the output picture signal, the plurality of pixels containing at least a pixel of a field of the input picture signal, the field being placed most chronologically adjacent to the considered field of the output picture signal, and
a pixel generating portion for generating each considered pixel of the output picture signal according to predictive information corresponding to the class decided by the class deciding portion and the plurality of pixels selected by the predictive pixel selecting portion.
The invention of claim 8 is a picture signal converting method for converting a field frequency of an input picture signal in the relation of M and N (where Mxe2x89xa0N; M and N are any natural numbers), comprising the steps of:
deciding a class for a considered pixel according to a plurality of pixels of the input picture signal, the plurality of pixels being decided according to the considered pixel in a considered field of an output picture signal, the plurality of pixels containing at least a pixel of a field of the input picture signal, the field being placed most chronologically adjacent to the considered field of the output picture signal,
selecting a plurality of pixels of the input picture signal, the plurality of pixels being decided according to the considered pixel in a considered field of the output picture signal, the plurality of pixels containing at least a pixel of a field of the input picture signal, the field being placed most chronologically adjacent to the considered field of the output picture signal, and
generating each considered pixel of the output picture signal according to predictive information corresponding to the class decided at the class deciding step and the plurality of pixels selected at the predictive pixel selecting step.
According to the present invention, the field frequency is converted by the class categorizing adaptive process. In the class categorizing adaptive process, using a teacher picture (equivalent to an output picture in the field frequency converting process) and a student picture (equivalent to an input picture in the field frequency converting process), a predictive coefficient that allows the sum of squares of errors of true values and predictive values to become minimum is defined. Thus, a picture having chronologically converted fields can be generated without need to detect a moving vector. Consequently, a large amount of hardware for detecting a moving vector is not required. In addition, since the field frequency converting process is performed by the class categorizing adaptive process, a large area is prevented from flickering because of a relatively low field frequency. Thus, a high quality picture can be provided.